Re: 1977 evinrude 115 water pump or impeller
Your father is probably right, and a new impeller is an excellent place to start.
The lower unit has to be removed in order to replace the impeller. Once you have the unit off, you can determine how much of the water pump needs to be replaced.
Seven screws need to be removed from the lower unit: two on each side, one in front of the trim tab, the one holding the trim tab, and one that is hiding above the trim tab.
The shift rod needs to be disconnected. The pin that holds it is under the carburetors. To release the pin, loosen the screw that forms the fulcrum of the bellcrank and spread the fingers of the bellcrank as shown in the thumbnail.
This is all covered in detail in the factory service manual; you should have one if you plan to do your own maintenance:
http://www.outboardbooks.com/index.cfm?fuseaction=search.main
